Lansing — Canadian oil giant Enbridge Inc. has agreed to pay for construction of a nearly four-mile tunnel beneath the Straits of Mackinac to house a replacement for its controversial Line 5 pipeline, Michigan officials announced Wednesday.

The agreement with Republican Gov. Rick Snyder’s administration anticipates construction of a shared “utility corridor” drilled 100 feet into bedrock below the lake bed, a project expected to take seven to 10 years and cost $350 million to $500 million.

It hinges on separate negotiations between Enbridge and the Mackinac Bridge Authority that the administration expect to be finalized before Snyder leaves office at the end of the year. The deal involves no taxpayer dollars, an Enbridge spokesman said.

The deal, if completed, would “provide permanent protection for our Great Lakes” by separating the Line 5 oil pipeline from direct contact with the water, said Michigan Department of Environmental Quality Director Heidi Grether.

She called it a “common-sense solution to a decades-long environmental concern.”

The deal requires Enbridge to take additional steps to reduce the risk of a spill during construction as it continues to operate Line 5, which carries up to 540,000 barrels a day of light crude oil and natural gas liquids through the Upper Peninsula and lower Michigan from Wisconsin to Ontario, Canada.

The "historic agreement" will eventually eliminate "nearly every risk" of an oil leak into the Straits, Snyder said, while allowing for multiple utilities to share the tunnel, "better connecting our peninsulas, improving energy security and supporting economic development."

But several environmental groups and activists blasted the deal. Snyder "cemented his disastrous legacy for the Great Lakes" with an agreement that will keep Line 5 operating for several years, said Sean McBrearty of Clean Water Action.

"Attempting to use the Mackinac Bridge Authority to bypass our environmental laws in this process is an insidious attempt by this administration to subvert democracy and risk 20 percent of the world’s fresh surface water so that a foreign oil company can continue to rake in massive profits," McBrearty said in a statement.

But the new agreement reflects the Canadian company’s commitment to protecting the Great Lakes and “makes a safe pipeline even safer,” said Enbridge spokesman Ryan Duffy.

“This is a win for anyone who wants to protect the Straits in the Great Lakes," Duffy said.

Deal has safety provisions

Under the deal, Enbridge must have staff on site capable of shutting down Line 5 within 15 minutes when waves reach a certain height. The company has also agreed to set aside $1.8 billion to respond to any potential Line 5 spill, a figure identified in a worst-case analysis performed for the state by researchers at Michigan Technological University.

The agreement aims to reduce the likelihood of a leak from the existing pipes while the tunnel is built and ensure close collaboration between Enbridge and the state after the new pipeline becomes operational, officials said. It also improves the safety of other Line 5 water crossings, Enbridge's Duffy said.

Among them: underwater inspections to detect potential leaks and evaluate pipe coating; placement of cameras at the straits to monitor ship activity and help enforce a no-anchoring zone, and steps to prevent leaks at other places where Line 5 crosses waterways.

The Detroit News first reported on developing plans for a shared utility corridor in June. The state has had initial discussions with other companies that own infrastructure currently sitting on the lake bed, including electric transmission cables damaged by an anchor strike in early April.

Enbridge’s feasibility study only assessed the possibility of housing the company’s own pipeline within the tunnel, Duffy said, but the technology is scaleable if officials decide to make the tunnel larger to accommodate other utilities. Those details will be decided during the ongoing discussions with the Mackinac Bridge Authority, he said.

“If at some point other utility companies were to join in and use the tunnel there would be discussions about potential cost sharing," Duffy told The Detroit News.

The Snyder administration and Enbridge both praised the agreement as a concrete to eventually decommission the Line 5 dual pipelines.The company, based in Calgary Alberta, insists they’re in good condition and could remain in place indefinitely but has been on the defensive in recent years following discoveries of dozens of spots where protective coating has worn off, plus damage from a ship anchor strike last April.

Enbridge “has operated Line 5 safely and reliably for decades” and cooperated with state regulators, Duffy said. But Snyder and other officials previously have accused Enbridge of being less than forthcoming — particularly about coating gaps on the submerged pipelines.

Michigan Environmental Council President and CEO Chris Kolb said the deal announced Wednesday leaves many unanswered questions about the fate of Line 5 during a project that could take "much longer" than 10 years to complete.

“The tunnel will take years to build and during that time the risk of a spill from the existing 65-year-old pipeline poses a very serious threat," he said in a statement. "At any moment, Line 5 could leak 2.4 million gallons of crude oil into the Great Lakes and cause billions of dollars of damage to our waters, coastal communities, and recreational economy.”

Could successor undo deal?

The deal, reached as Snyder’s term winds down, is sure to be a contentious issue in the campaign to succeed him. Democratic nominee Gretchen Whitmer has pledged to shut down Line 5 if elected governor in November. Her Republican opponent, state Attorney General Bill Schuette, has endorsed the tunnel option.

Both candidates were briefed on the agreement, said Michigan Department of Environmental Quality Director Keith Creagh.

It wasn’t immediately clear whether the next administration would have the legal authority to undo the agreement. Michigan owns the straits bottom lands and granted Enbridge an easement when the pipes were laid in 1953. Creagh said any effort to revoke it would trigger a lengthy and expensive court battle.

The deal calls for negotiating a public-private partnership between the company and the Mackinac Bridge Authority, the state agency that oversees the suspension bridge traversing the straits between Michigan’s upper and lower peninsulas near the underwater pipes.

Enbridge would build the shared utility tunnel, transfer ownership to the authority and then lease it back for 99 years. While details are still being worked out, “the intent is for Enbridge to be responsible for the operation and maintenance of that tunnel,” Creagh said.

If the Bridge Authority declines to be part of the deal, “it certainly would put this agreement relative to the tunnel aspects into question," he said.